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DTC codes / Chrysler codes / P1145

P1145 · ChryslerHO2S Cross Counts Bank 1 Sensor 3

P1145 on Chrysler vehicles indicates that the powertrain control module (PCM) has detected an abnormal number of cross counts from the downstream heated oxygen sensor (HO2S) on bank 1 sensor 3. Cross counts measure how frequently the sensor's voltage switches between rich and lean thresholds, and an excessive rate suggests the sensor is reacting to conditions it should not see or is failing internally.

SystemPowertrain
Code typeChrysler specific
SeverityMedium
Fix difficultyIntermediate
AreaFuel and air metering

Symptoms you may notice

  • Illumination of the check engine light, often with no other noticeable symptoms
  • A slight decrease in fuel economy over time
  • Occasional rough idle or hesitation during light acceleration
  • Failed emissions inspection due to readiness monitors or stored fault
  • In rare cases, a sulfur or rotten-egg smell from the exhaust if the sensor is misreporting

Common causes, most likely first

  1. Failed downstream heated oxygen sensor (bank 1 sensor 3) due to contamination or age
  2. Exhaust leak upstream of the sensor allowing outside air to pulse past the sensing element
  3. Wiring damage or poor connection at the sensor harness or PCM connector
  4. Excessive oil or coolant consumption contaminating the sensor element
  5. PCM software calibration issue or internal driver fault for the sensor heater circuit
  6. Restricted exhaust or catalytic converter damage altering exhaust pulses

How to diagnose and fix it

  1. Inspect the sensor wiring and connector for chafing, corrosion, or loose pins, and repair as needed
  2. Check for exhaust leaks between the engine and the sensor using a smoke test or visual inspection
  3. Monitor live data for bank 1 sensor 3 cross counts and compare with bank 1 sensor 1 to confirm the fault
  4. Test the sensor heater circuit resistance and supply voltage to rule out a heater fault
  5. Replace the downstream heated oxygen sensor if cross counts remain abnormal after wiring and leak checks
  6. Clear the fault codes and verify the repair by completing a drive cycle and rechecking cross counts
  7. If the code returns, inspect the catalytic converter for efficiency and replace if necessary

Cross counts reveal sensor behavior

  • A downstream oxygen sensor that is switching rapidly often indicates the catalytic converter is not storing oxygen properly, so the sensor may be reporting a real converter problem rather than being faulty itself.
  • Exhaust leaks that draw in outside air can create false lean readings and drive cross counts up, and these leaks are frequently missed because they are small and only appear under certain engine loads.
  • Chrysler PCMs can set P1145 from a momentary glitch, so a single occurrence should be verified with a full drive cycle before replacing parts.
  • Oil or coolant contamination from internal engine leaks can coat the sensor and cause erratic cross counts, so always check for consumption issues before installing a new sensor.
  • The downstream sensor on bank 1 sensor 3 is often located after the catalytic converter on V6 and V8 engines, and its cross counts are used to infer converter efficiency, meaning a converter fault can masquerade as a sensor fault.

Can I keep driving with P1145?

You can usually continue driving with P1145, but avoid long trips or heavy loads until the fault is diagnosed because a failing sensor or converter can worsen emissions and fuel economy. If the check engine light starts flashing or you notice misfire symptoms, stop driving and seek service immediately.

Tools that help

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Guidance is general and written for Chrysler vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

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